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🏏 The 18-Day DSA Cover Drive | Day 2: Meet Python's Counter

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🏏 The 18-Day DSA Cover Drive | Day 2 — Meet Counter

Learn DSA one Python trick at a time.

What's up, DEV community! 👋

Welcome back to Day 2 of The 18-Day DSA Cover Drive.

🏆 Kohli Corner

Fastest to 8,000 ODI Runs

Virat Kohli didn't score 8,000 ODI runs in a single innings.

He reached the milestone by scoring one run at a time, trusting the process, and showing up consistently.

Just like great innings are built one run at a time, great code is built one improvement at a time.

📊 Day 2 — Meet Counter

🎯 Today's Python Power-Up

Yesterday, we learned how to build a Frequency Map manually.

freq = {}

for item in arr:
    freq[item] = freq.get(item, 0) + 1
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It works.

It's clean.

But Python says...

"Why write four lines when one line is enough?" 😄

Meet Counter.

✨ The Magic Line 

from collections import Counter

arr = [1, 2, 1, 3, 2, 1]

freq = Counter(arr)

print(freq)
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Output

Counter({1: 3, 2: 2, 3: 1})
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That's it!

No loop.

No .get().

No if-else.

Just one line.

🤔 Imagine This...

Your teacher asks,

"How many students are wearing blue?"

❌ Yesterday's Way

You walk around the classroom and count everyone manually.

Again.

Again.

Again.

✅ Today's Way

The teacher presses a button on a smart attendance machine.

Blue  → 8
Black → 12
White → 6
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Instant result.

That's exactly what Counter does.

❌ Before 

freq = {}

for item in arr:
    freq[item] = freq.get(item, 0) + 1
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✅ After 

from collections import Counter

freq = Counter(arr)
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✅ Cleaner

✅ Smaller

✅ More Pythonic

🚀 Bonus Powers of Counter

Count a specific element 

print(freq[1])
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Output

3
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Find the most frequent element 

print(freq.most_common(1))
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Output

[(1, 3)]
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Pretty cool, right? 😄

💡 Where is Counter useful?

You'll commonly use it in problems like:

  • Finding duplicate elements
  • Counting character frequencies
  • Valid Anagram
  • Majority Element
  • Top K Frequent Elements
  • Frequency-based array problems

⚡ Interview Insight

Should you always use Counter?

✅ Use Counter when the problem is mainly about counting frequencies.

❌ Don't immediately use Counter if an interviewer specifically asks you to implement the frequency map yourself.

Understanding how Counter works internally (which we learned on Day 1 using dict.get()) is just as important as knowing the shortcut.

First learn the logic. Then learn the shortcut.

🧠 Quick Challenge

Without running the code...

Can you guess the output?

from collections import Counter

word = "mississippi"

freq = Counter(word)

print(freq["s"])
print(freq.most_common(1))
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👇 Drop your answer in the comments before checking!

🎯 Bonus Question

Can you think of another DSA problem where Counter can replace an entire counting loop?

I'd love to hear your answers!

🏏 Cover Drive of the Day

🏏 Concept: Counter

⭐ Python Gem: collections.Counter

💼 Interview Insight: Learn the logic first, then use the shortcut.

⏭️ Next Innings: defaultdict — A dictionary that creates missing keys automatically.

💬 Let's Discuss

Have you used Counter before?

Or did you learn something new today?

If you know another hidden Python gem that makes DSA easier, drop it in the comments! 👇

18DayDSACoverDrive | Python | DSA | Beginners | Learning

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